1. Field of the Invention
The invention relates in general to respirators and in particular to a new and useful closed-cycle breathing apparatus and gas mask for operation under pressure with a pressurized gas source supplying respiratory air and with an air bag being under prestress during the inspiration phase, and prestress means for prestressing the airbag said prestress means decreasing the amount of prestressing applied or decreasing the degree of prestress by means of a control element recognizing the expiratory phase, to thereby support the respiration during the expiration phase.
In a closed-cycle breathing apparatus and gas mask for operation under pressure it is guaranteed that the pressure in the breathing cycle is constant with regard to the surrounding atmosphere, so that no pollutants can enter the breathing cycle. The pressure applied by the prestress means can be generated by an elastic element for prestressing the air bag, by means of a mechanical/ pneumatic spring, such as is represented e.g. in German Patent DE-PS 31 05 637. As the prestressing of the air bag generated by the mechanical and pneumatic spring, is also maintained during the exhalation process, exhalation in such a system is rendered even more difficult due to the flow resistance to be overcome during the expansion in the expiration phase. The breathing resistance tends to increase.
From German Patent DE-OS 34 29 345 a closed-cycle breathing apparatus is known and a gas mask for operation under pressure wherein the pressurized gas source also supplies an auxiliary device increasing the mechanical prestressing of the air bag to achieve an increase in pressure. A detector connected to a measuring circuit differentiates between the respiratory phases and controls the auxiliary device during the exhalation phase so that the additional pressure exerted on the air bag is reduced.
In certain cases a simplified execution of the breathing support is desirable which is based exclusively on pneumatic/ mechanical elements without electronic control circuitry and without an additional electrical energy source.